Omnirange beacon antennas



y 31, 1950 A. M. CASABONA ETAL 2,939,141

OMNIRANGE BEACON ANTENNAS Filed Sept. 25, 195a 36 R g cam 5 0 "00001760 com os/r5 (URI EA COMPOSITE INVENTORS ANMNYMCASABO/VA 1 JAMES 5. man BY cousm/vm/o wowsm AGENT United States Patent OMNIRANGE BEACON ANTENNAS Anthony M. Casabona, Clifton, and James S. Engel, Tenafly, N.J., and Constantino Lncanera, Blauvelt, N.Y., assignors to International Telephone and Telegraph Corporation, Nutley, N.J., a corporation of Maryland Filed Sept. 25, 1956, Ser. No. 612,913

9 Claims. (Cl. 343-754) This invention relates to omnirange beacon antennas and more particularly to directive antenna systems for producing a multiple modulation radiation pattern having a fundamental modulation frequency and a harmonic of the fundamental frequencies for use with omnidirectional beacons.

Omnidirectional beacon systems are known having a high order of directional accuracy which is dependent upon the use of a directive antenna pattern rotated at a fundamental frequency, said pattern including a harmonic of this fundamental frequency so as to produce a generally multilobed rotating directive radiation pattern. Due to the rotation of the multilobed antenna pattern, a receiver located remotely from the transmitter receives energy which appears as an amplitude modulated wave having a fundamental modulation component and a harmonic modulation component. Reference signals related to the fundamental and harmonic frequency modulation respectively are transmitted omnidirectionally for comparison with the received components of the rotating pattern so that the receiver may determine its azimuth relative to the beacons antenna system. Such a radiation pattern is used in the navigational system known as TACAN and described in Electrical Communications, for March 1956, pp. 33-59.

Other antenna systems known to the prior art have disclosed the production of the modulation frequencies by the rotation of parasitic elements about a vertically disposed central radiator or radiators. Long straight wires and equivalents thereof have been used as parasitic elements. It has been found that in such prior art antenna systems the modulation level tends to decrease rapidly with vertical angle. Furthermore the radius of rotation, purity of modulation and vertical coverage were not independent, thereby requiring compromise in design.

An object of this invention is to provide an improved omnidirectional beacon antenna system especially suited for use in the radiation of a rotating multilobed directive radiating pattern.

Other objects of this invention are to provide an antenna system for producing a multilobed azimuthal directive pattern which does not utilize rotating radio frequency joints, which is reduced in complexity, which will have a reduced size and weight and which may be completely enclosed so as not to be affected by weather elements.

In accordance with one of the features of this system; our antenna system comprises a plurality of horn radiators each having an entrance or input portion and an exit or output portion disposed circularly about a vertical axis and extending radially therefrom to position the exit portion of the radiator for outward radiation. The entrance portion of each of the radiators are in juxtaposition to a common excitation means for cophasal excitation 'of the radiators to produce a multilobed radiation pattern. The horn radiators and a given portion of the common excitation means are rotated about the vertical axis to produce a rotating multilobed directional radiation pattern. I v

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Another feature of this invention includes a single antenna element centrally located of a plurality of circularly disposed horn radiators to excite a distributor for cophasally exciting each of the horn radiators. All of the elements of the system except the single antenna element are rotated to provide the desired radiation pattern of the TACAN type.

Still another feature of this invention includes a circular waveguide centrally excited disposed centrally of a pluarity of circularly disposed horn radiators and in coupling relationship with each of the radiators and arranged to feed different amounts of energy to the different horn radiators so as to produce a directional pattern. In an embodiment there is provided a cylinder of dielectric material having a varying wall thickness and having a central opening therethrough disposed eccentrically with respect to the central axis of the circular Waveguide to cooperate in cophasal excitation of each of the horn radiators and which feeds different amounts of energy to the different horn radiators.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective view with the top removed of an antenna system in accordance with this invention;

Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. 1 with the top in place; and

Fig. 3 illustrates radiation patterns useful in explaining the operation of this invention.

It is obvious that on the horizon, the component of motion is equal to the diameter of the rotating cylinder.

Referring to Figs. 1 and 2, the improved antenna system of this invention comprises a plurality of horn radiators 1 radially disposed to provide a circular configuration about a central electromagnetic energy distributor 2 including a circular waveguide 3 closed at the top 3a and bottom 3b thereof and an excitation means 4 disposed along the central axis of circular waveguide 3 and the circular configuration of horn radiators 1. The entrance portion 5 of radiators 1 are disposed adjacent to the central distributor so that the distributor 2 may couple energy to radiators 1 with cophasal energy. The exit portion 6 of radiators 1 are disposed for outward radia- .tion therefrom of the energy cophasally distributed to each of the radiators 1. The energy is coupled from distributor 2 through openings or irises 7 in the peripheral wall of waveguide 3 disposed to be in coupled relation with entrance portion 5 of radiators 1.

In employing the antenna system of this invention a signal is received at a remote point predominately from one source at a time and modulation is accomplished by the rapid interchange of sources and by virtue of their directivity. -Fig. 3 illustrates patterns obtained when nine horn radiators 1 are arranged in a circle. Each radiator 1 independently radiates a single cophasal lobe of energy resulting in the pattern illustrated in curve B, Fig. 3. The lobes of energy radiated by each radiator 1 have negligible side lobes. In the embodiment disclosed herein the radiators 1 are placed symmetrically so that the lobes occupy positions 40 degrees apart. The horn aperture or exit portion 6 and the result beam width is chosen so that the patterns overlap slightly at points midway between two maximums resulting in the radiation pattern illustrated in curve A, Fig. 3.

It is obvious to one skilled in the art that if the pattern of curve A, Fig. 3 were rotated, an observer at a fixed point would receive a modulated pattern. Starting at sum of the overlapping patterns of the individual radiator radiations. The percentage of modulation, therefore, would depend upon the extent of the overlap. If the exit portion 6 of each horn were made large enough, the beam width would be reduced to the point where no overlapping occurs. In this case the minimum would be zero and 100 percent modulation would be produced. Since the horn radiators 1 are arranged in a circular configuration, with adjacent edges touching, a change in horizontal dimension of portion 6 corresponds to a change in diameter. Hence, in this antenna system the diameter becomes the variable for the adjustment of depth of modulation. This adjustment is essentially independent, since a change in diameter does not substantially vary the purity or frequency of modulation.

Since the modulation is performed by the rapid scanning of individual lobes of energy, no theoretical limit exits in vertical coverage. All that is required is that the individual horn radiators I maintain their horizontal pattern and provide sufiicient energy at high angles for reliable reception. Realistically, however, it should be realized that at 90 degrees vertical angle equal amounts of radiation must simultaneously be received from all radiators if symmetry exists. Under these conditions the modulation level remains constant with rtation and no modulation exists. Hence, in practice it can be expected that the modulation level will fall some what with vertical angle but at a much lesser rate than antennas of prior art. At very high angles, depreciation in modulation may result from leakage of the horn radiators.

The uptilt and gain of the antenna system of this invention are dependent upon the vertical dimensions of exit portion 6 of the horn radiators. Since range has offered little difiiculty to date, and with the utilization of high powered transmitters, it seems advisable to use less gain in the antenna, thereby permitting less height. It is estimated that the antenna of this invention could be limited to one foot in height for the rotating RF section. To produce uptilt, the horn radiators would be elevated slightly above the horizon so as to place the maximum part of the vertical lobe above the horizon. It should be noted that no serious theoretical limitations exist on the vertical dimension of exit portion 6 of the horn radiators and that additional gain and uptilt can be accomplished simply by permitting additional height. As an alternative, two or more layers of small vertical dimension horns for exit portion 6 can be stacked vertically to produce the desired result.

Since the beam width of the horn will vary with frequency, it is expected that some changes in percent modulation may occur. With proper choice of =horn radiator aperture, however, it is felt that this variation can be kept within presently acceptable limits.

The low frequency modulation or 15 cycle modulation is accomplished in the system of this invention by proper distribution of energy to horn radiators 1. If the energy is varied sinusoidally in adjacent horns, the high frequency or 135 cycle modulation will become superimposed npon the fundamental rotation frequency. Electrically, this distribution of energy can be accomplished by various means including dampers, slots, or dielectric materials. The latter is illustrated in Figs. 1 and 2 by the ring of lossy dielectric material 9. The ring of lossy dielectric material of varying thickness has its opening eccentrically related to the central axis of waveguide 3, the axis upon which excitation means 4 is disposed. The excitation of each horn is then controlled by the amount of thickness of dielectric material between its feed point and the periphery of circular waveguide 3. This results in a radiation pattern substantially as illustrated in curve C, Fig. 3. The thickness of material 9 can be adjusted so that the variation in modulation level progresses sinusoidally among the nine radiators 1 when rotated. In

such a system, the relative phase of the cycle and 15 cycle components is adjusted by turning the dielectric ring 9 within the circular waveguide 3. This method, therefore, offers the advantage of simplicity, avoidance of metallic contacts, and ease of adjustment.

For proper operation, the excitation of each horn radiator 1 must be controlled so that the energy is cophasal. This is accomplished in the embodiment of Figs. 1 and 2 by the central probe excitation means 4 which excites circular waveguide 3. Waveguide 3 in turn distributes the electromagnetic energy to the plurality of horn radiators I placed about the periphery 1 of waveguide 3. The central excitation means 4 comprises a simple dipole 10. This is made possible by disposing bearings (not shown) between the stationary dipole 10 and the rotating waveguide-horn radiator assembly. The rotation is accomplished by a device such as by motor 8. In order to avoid discontinuity and possible leakage, a choke joint (not shown) may be necessary between the stationary dipole and the rotating assembly. However, such joints are extremely simple in design and offer no problem.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. An antenna system comprising a plurality of horn radiators having an entrance and exit portion, the entrance portion of each of said radiators being disposed radially about a central axis to form a central area, an electromagnetic energy distributor including a hollow dielectric body having varying wall thickness disposed coaxially of said central axis in said central area to distribute electromagnetic energy cophasally to each of said radiators to provide a multilobed radiation pattern, means disposed within said central area for exciting said distributor with electromagnetic energy, and means to rotate said radiators and said distributor about said central axis to provide a rotating multilobed directional radiation pattern.

2. An antenna system comprising a circular waveguide disposed coaxially of a vertical axis, a plurality of horn radiators disposed radially with respect to said axis about the peripheral surface of said waveguide, said peripheral surface having means in coupled relation with said radiators for coupling energy thereto, means including a hollow dielectric body having varying wall thickness disposed within said waveguide to excite each of said radiators cophasally with electromagnetic energy to provide a multilobed radiation pattern, and means to rotate said waveguide and said radiators about said axis to provide a rotating multilobed directional radiation pattern.

3. An antenna system comprising a circular waveguide disposed coaxially of a vertical axis, a dipole antenna disposed on said axis to excite said waveguide with electromagnetic energy, a plurality of horn radiators disposed radially with respect to said axis about the peripheral surface of said waveguide, said peripheral surface having irises therethrough in coupled relation with said radiators for coupling energy thereto, a dielectric body disposed to fill said waveguide having an opening therethrough eccentrically disposed with respect to said axis to distribute energy cophasally to each of said radiators to provide a multilobed raidation pattern, and means to rotate said waveguide and said radiators about said dipole antenna to provide a rotating multilobed directional radiation pattern.

4. An antenna system comprising a plurality of horn radiators, each of said radiators being disposed in a circular configuration radially of a vertical axis, means including a hollow dielectric body having a varying wall thickness disposed centrally of said configuration common to each of said radiators to feed energy to each of said radiators cophasally to provide a multilobed radiation pattern, and means to rotate said radiators about said axis to provide a rotating multilobed radiation pattern.

5. An energy translator comprising an input means disposed on a given axis, a circular waveguide disposed coaxially of said axis, a plurality of output means spaced about the periphery of said waveguide, and a dielectric cylinder disposed in said waveguide having a varying wall thickness between the waveguide and the input means to control the coupling of cophasal energy to said output means.

6. An energy translator comprising an energy input probe, a circular waveguiding structure closed at each end thereof disposed coaxially of said probe and rotatable thereabout, a plurality of output means spaced about the periphery of said waveguide, a dielectric ring of irregular wall thickness in said waveguide having its axis disposed parallel to said probe to modulate the cophasal energy coupled to said output means, and means to rotate said waveguiding structure and said dielectric ring about said probe.

7. An energy translator comprising a circular waveguide, means to energize said waveguide, a plurality of horn radiators spaced about the periphery of said waveguide, means electrically coupling each of said radiators to said waveguide for cophasal energy distribution to said radiators, a dielectric cylinder disposed in said waveguide having a wall of varying thickness between said energizing means and the wall of said waveguide to modulate the distributed energy.

8. An energy translator comprising a circular waveguide closed at each end thereof, a plurality of horn radiators spaced about the periphery of said waveguide, means energizing said waveguide, an energy coupling iris disposed in the wall of said waveguide in communication with each of said radiators for cophasal energy distribution to each of said radiators from said waveguide, a dielectric cylinder disposed in said waveguide having a wall of varying thickness between the waveguide and said energizing means to amplitude modulate the distributed energy and means to rotate said waveguide, said dielectric cylinder and said radiators relative to said means energizing.

9. An antenna system comprising a circular waveguide disposed coaxially of a vertical axis, means to excite said waveguide with electromagnetic energy, a plurality of horn radiators disposed radially with respect to said axis about the peripheral surface of said waveguide, said peripheral surface having means in coupled relation with said radiators for coupling energy thereto, a dielectric body disposed to fill said waveguide having an opening therethrough eccentrically disposed with respect to said axis to distribute energy cophasally to each of said radiators to provide a multilobed radiation pattern and means to rotate said waveguide and said radiators about said means to excite to provide a rotating multilobed directional radiation pattern.

References Cited in the file of this patent UNITED STATES PATENTS 2,369,808 Southworth Feb. 20, 1945 2,413,085 Tiley Dec. 24, 1946 2,461,005 Southworth Feb. 8, 1949 2,549,721 Straus Apr. 17, 1951 2,567,220 Litchford Sept. 11, 1951 2,599,896 Clark et a1. June 10, 1952 2,677,766 Litchford May 4, 1954 

